Objective To study the antitumor effects of dendritic cell vaccine induced by astragalus polysaccha?rides on S180 tumor-bearing mice, and its possible mechanism. Methods Dendritic cells derived from mouse bone marrow were induced maturation by astragalus polysaccharides and loaded with S180 tumor antigen to prepare tumor vaccine. Tu?mor-bearing mice were divided into four groups and treated on day-5 and day-10 respectively. Group A was injected with NS, Group B with CTX (50 mg/kg), Group C with dendritic cells induced by astragalus polysaccharides and Group D with dendritic cells induced by tumor necrosis factor (TNF)-α. After 12 days of tumor-bearing, the animals were killed. The sub?cutaneous sarcoma, thymus and spleen were separated and weighted. The inhibitory rate, thymus index and spleen index were then calculated. ELISA assay was used to detect the levels of interleukin (IL)-4, interferon (IFN)-γin serum of tumor bearing mice. Results The tumor inhibition rate was higher in astragalus polysaccharide group and cytokine group than that of CTX group (64.25%, 64.10%vs 35.11%). The thymus index was higher in astragalus polysaccharide group and cyto?kine group than that of CTX group (1.69 ± 0.26, 1.74 ± 0.38 vs 1.45 ± 0.22). The spleen index was higher in astragalus poly?saccharide group and cytokine group than that of CTX group (5.44 ± 0.76, 5.31 ± 0.81 vs 3.54 ± 0.52). The level of IL-4 was lower in astragalus polysaccharide group and cytokine group than that of CTX group (15.66±2.57, 14.72 ± 4.84 vs 23.95 ± 6.07). The level of IFN-γwas higher in astragalus polysaccharide group and cytokine group than that of CTX group (16.54 ± 3.71, 17.20 ± 2.03 vs 10.37 ± 2.19). All the differences were statistically significant (P<0.05). Conclusion Dendritic cell vaccine induced by astragalus polysaccharides can effectively inhibit tumor growth. Its mechanism may be associated with the promotion spleen index and thymus index of S180 tumor-bearing mice, the effective correction of Th1/Th2 imbalance in?duced by tumor, and the enhancement of antitumor immune responses.